During underwater training carried out in scuba diving courses, the pupils are required to warn the instructor when the pressure in the compressed-air tanks has dropped below 100 bar, and subsequently 50 bar. Since a single instructor is normally required to keep an eye on a team made up of a number of pupils, it is important that all the pupils may be able to communicate their datum to the instructor in the shortest time possible.
From the U.S. Pat. No. 5,357,242 a pressure gauge is known for detecting the pressure of the air in a compressed-air tank provided with an acoustic and optical alarm system, and with an adjustable alarm pointer which can be set at the pressure at which the alarm signal is activated. When the air pressure in the compressed-air tank reaches the alarm pressure limit set, an electric circuit closes and activates the alarm.
This device enables the setting of a single alarm pressure, and since it is adjustable, it can easily be tampered with; consequently, it is not very suitable for use in training courses.
From the U.S. Pat. No. 4,800,373 an alarm device is known, which is both acoustic and optical and suitable for detecting the pressure in a compressed-air tank; this device comprises a two-stage alarm system capable of indicating an initial low pressure and then a subsequent low danger-level pressure.
However, both these known devices are unsuitable for detection at a distance by an instructor who must monitor simultaneously a team of divers.